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Comma after a Period — The Complete Guide

Comma after a Period — The Complete Guide

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Using punctuation marks is nothing short of confusing, taxing, and even time-consuming; blame this on the variation among the rules in writing style guides.

Language is inherently arbitrary, and writers have the prerogative to calibrate their writing style to make their inner thoughts visible to readers.

So today, we’ll try to focus our sense-making on the adjacent period-comma placement to make things clearer.


When do we need a comma after a period?

A comma after a period is necessary when the period ends an abbreviation in a list, introductory expression, parenthesis, salutation, compound sentence, and inverted complex sentence. But, no comma is needed when the abbreviation is used as a name title or prefix, essential sentence element, and suffix.


Placing the necessary comma after a period

Placing a comma after a period can look awkward, especially if it is done midsentence.

This is so because we are preconditioned to the terminal function of periods or full stops as per the Brits.

Albeit a bit of an eyesore, certain circumstances entail the necessary comma placement after a period.

Let’s look at each of them in detail.


When the period is part of an abbreviation in a list

At least in American English (AmE) and its followers, the convention is to place periods in abbreviated words, whereas British English practices period omission.

If you’re quite keen on comma placement rules, you must already know that a serial list needs to be chunked with commas.

This meanwhile suggests that when an abbreviated word comes in a list, particularly in the realm of AmE language use, a comma is also expected to come afterward.

Here’s an example to illustrate the explanation.

Allen, M.C., Andrew, and Eric went to the same high school.

Furthermore, AmE also suggests placing a post-comma when the abbreviation is listed before the conjunctive device, such as “and” in the previous example.

Allen, Andrew, M.C., and Eric went to the same high school.


When the abbreviation comes at the end of an introductory expression

Another case that essentializes the comma placement after a period is when the abbreviated word comes at the end of an introductory statement.

Introductory expressions can be as short as a word and as long as a clause; hence, it is needless to say that a comma should be placed whenever the abbreviated term ends the sentence’s introduction.

Here’s an example to represent the explanation.

Around the end of Oct., we’re planning to have a reunion.

Note, though, that abbreviations are generally frowned upon in formal writing, so avoid using one when it is inappropriate.


When the abbreviation comes before a parenthesis

The next case the requires a comma after a period is when the abbreviated word comes before what we refer to as “parenthetical information.”

In stylistics, a parenthesis is a statement that is inserted to convey emphasis to drive rhetoric or persuasion.

As these elements are non-essential to the overall grammaticality of the sentence, they are set off with commas to signal the reader of such implication.

You can refer to the next sentence as an example.

My friend A.J., who’s a diagnosed alcoholic, ironically got hit by a drunk driver.

Remember that removing a parenthesis does not lacerate the sentence’s grammatical structure, thereby making it nonrestrictive to the whole unit of meaning suggested by the leftover information.

And, of course, when this happens, you can already drop your commas.

My friend A.J. ironically got hit by a drunk driver.


When the abbreviation ends a parenthesis

Since we’ve already understood what parentheses are, the rule in this subsection should be a lot easier to digest.

We have previously known that parenthetical information needs to be encapsulated with commas, particularly when it appears midsentence.

Apparently, it should also follow that a post-comma is necessary if the abbreviated word is the last element in the parenthesis.

Look at this one.

George’s success in the B2B market can be attributed to strong organizational systems, not to mention his great mgmt., as well as his engagement strategies.


When the abbreviation in itself is a parenthesis

Sometimes, the abbreviated term per se serves as the only parenthetical element, especially those Latin abbreviations that are still commonly used to date.

A post-comma is also necessary when parenthetically inserting common Latin abbreviations like “etc.,” “e.g.,” and “i.e.”

Here’s an example.

Previous board members, e.g., Peter Dutton, Robert Schultz, and Ryan Anderson, were against that idea.

The sentence above may also be represented in another way, particularly by enclosing the examples in parenthetical marks.

Previous board members (e.g., Peter Dutton, Robert Schultz, and Ryan   Anderson) were against that idea.

Bear in mind, once again, that abbreviations should be avoided in formal writing; otherwise, feel free to truncate your words.


When the abbreviation is a salutation

Salutations are introductory remarks used in e-mails or letters. They are used to inform the reader as to whom the message is directed.

When you want to use the abbreviated version of the company or person’s name in your salutation, a post-comma is expected to come afterward.

Always remember not to place your comma after adjectives like “dear” or “dearest.”

Dear E.J.C.,

Dearest K.D.,


When the abbreviation is in a compound sentence

The essential comma placement can also be attributed to default sentence structure rules, just like in compound sentences.

A compound sentence is made up of two independent clauses linked by coordinating conjunctions which are also known as the FANBOYS.

Experienced writers know that the rear independent clause must be preceded by a comma, and thus, the same comma placement rule applies when the abbreviated word appears at the end of the initial clause.

Also remember that the comma comes before the conjunction rather than after.

New York City has the densest population in the U.S.A., and Greater London is also its equivalent in the U.K.


When the abbreviation is in a reversed-order complex sentence

A rule still related to sentence structure, an abbreviated word that comes at the end of the frontal clause in an inverted complex sentence needs a post-comma too.

A complex sentence is made up of at least one dependent and one independent clause, in which the independent clause initially appears in the regular structure.

Conversely speaking, a reversed-order complex sentence is a type of structure in which the dependent clause comes first.

While a comma is unnecessary in a regular structure, we do need a comma in the inverted type.

(Regular) Life was so different when we lived in the U.S.A.

(Reversed) When we lived in the U.S.A., life was so different.


The incorrect comma after a period

Now that we’ve seen when to place necessary commas after a period with respect to syntactic and stylistic rules, we had better look at the instances where the post-comma placement becomes incorrect.


Name titles followed by the person’s name

First, it is incorrect to place a comma if the name title or honorific is subsequently followed by the actual name of a person.

A name title serves as a prefix to the name, mostly with a polite implication, which means it is a crucial element in effectively expressing polite language use.

No comma should be placed between the name title and the actual name of the person no matter where it appears within the sentence.

(Correct) The school librarian is Mr. Calvin Smith.

(Incorrect) The school librarian is Mr., Calvin Smith.

The sentence-essential abbreviation

If the abbreviation is used as an essential part of the sentence, such as a subject or an object, no comma should be placed after the period that ends the abbreviated term.

When used in such situations, placing a comma after the abbreviated word’s period becomes incorrect.

Consider the examples below.

(Correct) Please bring a valid I.D. with you.

(Incorrect) Please bring a valid I.D., with you.


When the abbreviation is used as a suffix

Units of measurements are also commonly abbreviated in English in which they are used after a certain numerical data, for example, kg., cm., and km.

These measurements serve as fixed suffixes to the quantitative data, and thus, no comma should be used after the abbreviation’s period.

This remains true, of course, so long that the abbreviated word does not fall under any of the necessary comma placement rules explained earlier.

Here’s an example for clarity.

I only used to weigh 50 kg. on average in my early twenties.

Actually, most people nowadays tend to drop the period after the abbreviated unit of measurements, so please feel free to do so if you want to.

But if you’re used to the traditional manner of writing, there isn’t any problem either, so long that the idea or thought is not lost.


Frequently Asked Questions on “Comma After a Period”


Is there a comma after the period in etc.?

When parenthetically used mid-sentence in a running text, a comma should come before and after “etc.,” for example, “The students’ demographics such as gender, age, citizenship, etc., were taken for record-keeping.”


Should there be a comma after the period in inc.?

When used in the running text, the default equation is to use a comma after the period in “inc.” when and if another comma also precedes it. This pre-comma usage leans more towards the traditional way of punctuating business name suffixes.


Does the period go after the parenthesis?

When the parenthetical information appears at the end of the sentence, the period should be placed outside or after the closing parenthetical mark.



Although punctuation often seems intimidating to most people, we had better express our gratitude for their existence.

Without them, textual data would be clunky, messy, unemotional, and even extremely difficult to read. 

So, the next time you get stuck in a similar or related concern, please don’t hesitate to refer to our humble page for clarity.